The present invention relates to a method of producing particles having a particle size of less than 100 nm and surface areas of at least 20 m2/g where the particles are free from agglomeration. The method involves synthesizing the particles within an emulsion having a 1-40% water content to form reverse micelles. In particular, the particles formed are metal oxide particles.
Nanometer-sized particles have a wide variety of applications including the areas of magnetic materials, heterogeneous catalysts, toner compositions, and ceramics. Typical techniques to synthesize these particles include sol-gel processing and emulsions.
Emulsions present a unique method to prepare nanometer-sized particles. Stable emulsions comprise a continuous phase and a discontinuous phase which are immiscible, where isolation of the discontinuous phase is accomplished by the use of surfactants. The discontinuous phase constitutes a substantially spherical regime which can potentially serve to control particle size. This phase is easily subjected to disruption, however, due to surface tension that exists between the immiscible phases. Thus, there exists a need for methods to obtain unique emulsion compositions that enhance stability of isolated phases and that yield particles having a desired size and morphology.
Metal oxide particles have previously been formed within micelles.
U.S. Pat. No. 5,725,802 relates to a process for the preparation of metal oxide particles. Water-in-oil microemulsions are formed in which the oil used is a perfluoropolyether, and metal ions in the aqueous phase are reacted with a gaseous or vapor reactant.
U.S. Pat. No. 5,670,088 relates to a method for forming mixed metal oxide particles. A microemulsions is used which includes a perfluoropolyether oil and a perfluoropolyether surfactant. The method further involves mixing one metal in an aqueous phase with a second metal in a perfluoropolyether oil phase. The addition of an alkali solution is accompanied by heating to form the desired oxide.
U.S. Pat. No. 5,695,901 relates to a method for producing nano-size magnetic iron oxide particles. An iron reactant is contained in a disperse phase, reacted with a basic reactant and subjected to a controlled oxidation by the addition of a oxygen-containing oxidant.
European Patent No. EP 0 370 939 relates to a process for producing ultrafine, magnetic neodymium-iron-boron particles. The particles are formed in an emulsion having a discontinuous aqueous phase, comprising an aqueous solution of neodymium-, iron- and boron-containing compounds, which is added to a continuous phase and an ionic surfactant to form an emulsion.
The present invention provides techniques for making very small particles of a variety of materials, small particles of material that can be made by the processing method, and methods of use of these particles.
One aspect of the invention provides a method for preparing a particle. The method involves providing an emulsion having a water content of about 1-40% and includes a hydrocarbon and at least one surfactant. The emulsion forms micelles which comprise a disperse aqueous phase. At least one reactant is added which reacts in and with the disperse aqueous phase to form a particle having a particle size of less than about 100 nm where the particle is free from agglomeration.
Another embodiment of the invention provides a method for preparing a particle from an emulsion having a water content of about 1-40% and includes a hydrocarbon and at least one non-ionic surfactant. The emulsion forms micelles which comprise a disperse aqueous phase. At least one reactant is added resulting in a particle having a particle size of less than about 100 nm where the particle is free from agglomeration.
Another aspect of the invention provides a method for coating a particle within a micelle. Preferred embodiments include coating the particle with a metal oxide layer.
In another aspect of the invention, a method is provided for drying an emulsion including nanometer-sized particles. The method includes the steps of forming an emulsion to prepare particles having a particle size of less than about 1 xcexcm and exposing the emulsion to a supercritical fluid to dry the particles.
Another method of the invention involves forming an emulsion to prepare particles having a particle size of less than about 1 micron, and exposing the emulsion to a supercritical fluid to dry the particles.
In another embodiment a method is provided that involves effecting a reaction in the presence of a reverse emulsion, and producing a material from the reaction having a particle size of less than about 100 nm. The material retains a surface area of at least about 100 m2/g when heated to 700xc2x0 C.
In another embodiment a method is provided that involves oxidizing hydrocarbons in the presence of one or more metal oxides. The metal oxides have an average particle size of less than about 100 nm.
In another aspect the invention provides a series of compositions. In one embodiment a composition is provided that includes a material having an average particle size of less than about 100 nm. The material retains a surface area of at least about 100 m2/g when heated to 700xc2x0 C.
In another embodiment a composition is provided that includes a material capable of catalyzing a combustion reaction of a hydrocarbon. The material has a surface area, after exposure to conditions of at least about 1300xc2x0 C. for at least about 2 hours, of at least 20 m2/g.
Other advantages, novel features, and objects of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings, which are schematic and which are not intended to be drawn to scale. In the figures, each identical or nearly identical component that is illustrated in various figures is represented by a single numeral. For purposes of clarity, not every component is labeled in every figure, nor is every component of each embodiment of the invention shown where illustration is not necessary to allow those of ordinary skill in the art to understand the invention.